If you install this component outside of a Symfony application, you must
require the vendor/autoload.php file in your code to enable the class
autoloading mechanism provided by Composer. Read
this article for more details.

The ExceptionHandler class catches
uncaught PHP exceptions and converts them to a nice PHP response. It is useful
in debug mode to replace the default PHP/XDebug output with something prettier
and more useful:

The DebugClassLoader attempts to
throw more helpful exceptions when a class isn't found by the registered
autoloaders. All autoloaders that implement a findFile() method are replaced
with a DebugClassLoader wrapper.